The liquid recirculating velocity V-lr and gas holdup epsilon(gr) in the riser of an air-water-silica-sands three-phase annulus airlift reactor (AALR) were studied in the present investigation. By considering the reactor consisting of four sections, a hydrodynamic model for three-phase AALRs was developed for the first time to simultaneously predict V-lr, and epsilon(gr) from only reactor geometry and operation parameters without prior knowledge of gas holdup in the riser and downcomer and superficial gas velocity in the riser. The model was experimentally validated using an AALR of 0.102 m i.d. and 2 m height that was designed and fabricated for this study. The liquid recirculating velocity in the riser was measured by the tracer analysis technique. The gas holdup in the riser was determined by the manometric technique. The effects of superficial gas velocity, solids concentration, and draft tube diameter on V-lr and epsilon(gr). were examined. The comparison between the experimental results and model predictions showed that discrepancies for V-lr and epsilon(gr) were within +/- 10% and +/- 20%, respectively. The model was also satisfactorily tested with the experimental results obtained by different authors in reactors with different geometries and operating systems.